THREE-DIMENSIONAL GEARS MODELLING IN MULTIBODY SYSTEMS ANALYSIS

We present a formulation for describing gear pairs in the three-dimensional analysis of flexible mechanisms. The set of holonomic and non-holonomic constraint equations that defines the behaviour of gears is developed. The formulation is capable of representing almost any kind of gears used in industry: spur gears, bevel gears, hypoid gears, etc. All reaction forces due to gear engagement are accounted for. Coulomb friction forces due to relative sliding motion are also considered. Gear trains and planetary systems can be easily modelled by superposing several gear pairs in the same system. © 1997 by John Wiley & Sons, Ltd.     

A unique mechanism of nuclear division in <i>Giardia lamblia</i> involves components of the ventral disk and the nuclear envelope

The fine structure of the binucleate, parasitic protist Giardia lamblia during interphase and divisional stages was studied by serial thin sectioning and three-dimensional reconstructions. The earlier sign of nuclear division is the development of a few peripheral areas of densely packed chromatin directly attached to the inner nuclear envelope. An intracytoplasmic sheet of ventral disk components grows from the cell periphery towards one of the nuclei, apparently constricting this nucleus, which becomes located at a ventral bulge. After the basal bodies become duplicated, a full nuclear division occurs in trophozoites, giving two pairs of parent-daughter nuclei. This full division occurs in a dorsal-ventral direction, with the resulting nuclear pairs located at the sides of the two sets of basal bodies. A new ventral disk is formed from the diskderived sheets in the cell harboring the four nuclei. Cytokinesis is polymorphic, but at early stages is dorsalto-dorsal. Encysting trophozoites show the development of Golgi cisternae stacks and dense, specific secretory granules. 3-D reconstructions show that cysts contain a single pair of incompletely strangled nuclei. The dividing Giardia lacks a typical, microtubular spindle either inside or outside the nuclei. The nuclear envelope seems to be the only structure involved in the final division of the parent-daughter nuclei.     

Mathematical modelling of the diffusion of ascorbic acid during water blanching of surface frozen potato strips

Partial freezing is a promising technique in producing good quality french fries, especially for potatoes stored for an extended period and containing large amounts of reducing sugars. The cell damage of the potato strip caused by surface freezing facilitates surface leaching of reducing sugars and other soluble solids like ascorbic acid, preventing undesirable dark colour in the finish-fried products. A theoretical study to describe the diffusion of ascorbic acid during the water blanching at 50°C of surface frozen potato strips (10 x 10 x 80 mm) is developed. Ascorbic acid profiles as a function of blanching time, position in the potato strip and thickness of the frozen layer are shown as well as average retention as a function of blanching time, frozen layer thickness, apparent diffusion coefficient and mass transfer coefficient of ascorbic acid. Significant changes in the ascorbic acid concentration during blanching are produced in the frozen layer. Ascorbic acid average retention is mainly influenced by frozen layer thickness and temperature, and the mass transfer coefficient is less important.     

Stream-Symmetry of Heat Exchangers and Heat Exchanger Assemblies

Sufficient conditions are given for a heat exchanger or an assembly of heat exchangers to be invariant under the interchange of the two fluids. Analysis of this symmetry is performed on tht basis of geometrical or topological properties of the exchanger, and no prior knowledge of the exchanger solution is required. The 1-2 and 1-4 TEMA E, the split-flow TEMA G, and the divided-flow TEMA J shell-and-tube exchangers are discussed as examples. A t tent ion is drawn to possible erroneous interpretations of published F-charts for stream-unsymmetric eases.     

CHANGES IN LIPIDS BOUND TO THE I-Z-I FRACTION RELATED TO THE MYOFIBRILLAR FRAGMENTATION INDEX (MFI) OF OVINE LONGISSIMUS DORSI STORED AT 4C

The lipids bound to the I‐Z‐I fraction and the Myofibrillar Fragmentation Index (MFI) of postmortem ovine Longissimus dorsi stored at 4C were investigated. At zero time of storage total lipids were composed of about 50% neutral lipid and 50% phospholipid. During storage, the neutral lipid fraction showed a significant decrease (P < 0,01) in the relative percentage of triglycerides and a significant increase (P < 0.01) in free fatty adds. The composition ofphospholipids extracted from I‐Z‐I with chloroform:methanol 2:1 (v/v) remained unchanged. Further treatment of the I‐Z‐I fraction with chloroform:methanol (2:1, v/v) containing 0.25% (v/v) of concentrated HCl extracted an additional amount of phospholipids. The content of phospholipid extractable from the I‐Z‐I fraction with acidified organic solvents significantly decreased (P < 0.01) during storage and this change was accompanied by a significant increase (P < 0.01) in the MFI.     

Fractions of a chloroform extract of ajenjo leaves (<i>Artemisia mendozana</i> DC. var. <i>mendozana</i>) inhibit the proliferation,viability and clonogenicity of B16-F0 melanoma cells

The ajenjo, Artemisia mendozana DC. var. mendozana (Asteraceae), grows in the Andean foothills of Mendoza and San Juan, Argentina, and is used as a medicinal plant for its antispasmodic and antifungal properties. The aim of this work was to obtain fractions of a chloroform extract of ajenjo leaves and to evaluate the in vitro effects on proliferation, viability and clonogenicity of B16-F0 melanoma cells. Using a silica gel chromatography column, 120 fractions were collected and grouped according to the chromatographic profile in 9 main fractions (F1–F9). Their major compounds identified were: terpenes (F1), terpenes and sesquiterpene lactones (F2–F3), sesquiterpenes (F4–F6) and phenols and sesquiterpenes (F7-9). B16-F0 cells were incubated for 72 h with DMSO (vehicle) or 0.1 mg/ml F1–F9. At 72 h of culture, F1 decreased both the growing index (GI) and cell viability. F2 and F3 both decreased GI and only F3 decreased clonogenic activity. F4 and F5 both decreased GI. Only F5 decreased cell viability and F4 decreased clonogenicity. Consequently, fractions F6–F8 did not affect any of the cell parameters assayed, while F9 decreased cell viability and inhibited clonogenicity.